(a) Field of the Invention
This invention relates to electron devices and in particular to quantum interference devices utilizing interference of electron waves within. Quantum interference devices usually utilize an external perturbation caused by a magnetic or electric field as well as optical interaction to modulate the electron wave interference.
(b) Description of the Related Art
A quantum interference device (QID) uses the interference of electron wave passing through at least two different channels. By using an external perturbation induced by a magnetic or electric field a different phase contribution is added in each channel thus resulting in a constructive or destructive interference of the electron wave as a function of the field intensity. Devices of this type are described in [1] Bandyopadhyay et al., IEEE IEDM86 1986, and in [2] EP0381591A2, [3] U.S. Pat. No. 5,371,388, [4] U.S. Pat. No. 5,157,467, [5] U.S. Pat. No. 5,521,735, all of which are incorporated herein by reference.
FIG. 1 is a quantum interference device in the prior art operated with a magnetic field. The intensity of the field is used to control the current passing through the QID. The initial electron wave propagates from a common channel 1 and into two separated channels 2 and 3 comprising a ring 4. The waves then converge back to a common channel 5 as the electron exits the device. A magnetic field marked B is induced inside the ring 4 as the electron pass through the device. An interference of the electron wave occurs once it converges back into 5. The magnetic field B affects the phase of sections 2 and 3, according to the Aharonov-Bohm effect, in a different manner due to inherent inhomogeneous structure of the material comprising ring 4, thus resulting in either a constructive or a destructive interference of the electron wave in section 5.
The Aharonov-Bohm (AB) effect is where the presence of a voltage potential V or magnetic field B affects the phase component of the electron wave function. The phase component of the electron wave is known to depend on the potential through the following relation:Δθ=2πe/ch·V·t Where e is the electron charge, h is Plank's constant, c the speed of light, Δθ is the phase gained for spending a time period t with potential V, or in the presence of magnetic flux Φ by:ΔΦ=2πe/ch·Φ
Referring to FIG. 2, the transport probability through the QID of FIG. 1 is shown as a function of the magnetic field B and area cross section A. When the phase difference between the two mentioned paths is an odd multiple of π, a destructive interference will occur and the transport probability will drop. On the other hand, when the phase difference is an even multiple of π a constructive interference will result in high transport probability and high current thus resulting in the depicted oscillations. The transmission factor |T|2 is given by:|T|2=cos2{e/(h/2π)·A/2·B}
FIG. 3 is a quantum interference device in the prior art [1] operated using an electric field. Two GaAs quantum layers 10 and 11 are layered with an AlGaAs barrier layer 12 between them, to form two conducting channels. Electrons traveling through the device from the source 6 to the drain 9 pass either through channel 10 or 11. Since the thickness of the barrier layer 12 is small at both ends, tunneling occurs between the layers 10 and 11 at both ends of said barrier. However, the thickness of the barrier 12 is large at the central portion, thus little tunneling happens there. A voltage can be applied to the central portion by using a gate terminal 7, and a potential difference ΔV can be induced between the two channels 10 and 11. As a result, the electron wave with vectors k1 and k2 traveling in the two channels have the following difference according to the electric AB effect:K1−k2=e·ΔV/(h/2πv Similarly the transmission factor is given by:|T|2=cos2{e·ΔV·τt/2(h/2π)}Where τt=L/ν is a time required for electrons to pass through channels 10 and 11 (as marked in FIG. 3) where ν is the velocity of the electrons. In this manner, the current through the QID is controlled by the electric field induced by the gate terminal 7 producing a potential difference ΔV.
FIG. 4 shows the current through the device of FIG. 3 as a function of the gate voltage. The current has an oscillatory behavior as a function of the gate voltage due to constructive and destructive interference of the electron waves resulting from the phase difference mentioned above. Lower drain voltages result in lower electron velocity ν thus affecting the oscillation period as shown.
FIG. 5 is a quantum interference device in the prior art [2] operated using an electric field. Electrons are injected from the source 21 and collected by the drain 31 as they travel through a confined passage. The passage is confined by a mean 28, implemented by a doping implant, to create a depletion region where electrons cannot enter, and by control terminals 25 and 32 inducing a depletion region using the field effect, thus resulting in two confined conduction channels 26 and 27 through which electrons can propagate. The terminals 22 and 33 are used to induce a different potential in the conduction channels 26 and 27 respectively. The voltage potential difference between the two channels results in a different phase acquired by the electron wave as it passes through each channel according to the AB effect. This phase difference is in direct proportion to the potential difference between terminals 22 and 23. The size of the confined region is kept lower than the inelastic scattering length of the electron in the material. As a result, an interference of the electron wave as a function of the said potential difference will occur, thus modulating the transmission through the channels and the source to drain current. The phase difference Δφ between the two electron waves respectively passing through the channel regions 26 and 27 is represented by:Δφ=(kF2−kF1)L=[(2m(EF−E0 2))1/2−[(2m(EF−E0 1))1/2]L/h Where L stands for the effective length of the channel regions 26 and 27 and the value of E0 1 and E0 2 represent the confined electron energy level modified by the terminals 25 and 32.
FIG. 6 is a cross section of the quantum interference device in the prior art [2]. The cross section is depicted along the line AA′ as shown in FIG. 5. The channel confinement implanted means is marked 40 with a resulting depleted region 41. The terminals 25a and 32a use the field effect to induce depletion regions 37 and 38 respectively. The layers marked as 34, 35 and 36 are constructed to yield a quantum well confining the electrons in the directions perpendicular to their wave vector by using AlGaAs and GaAs respectively. As a result the electron energies (E0 2 and E0 1) are quantized inside the well and having their energy above the Fermi level EF.
FIG. 7 depicts a quantum interference device in the prior art [3] operated using an electric field. The layers marked in the structure as 46, 47 and 48 are used to create a quantum well to confine electrons thus forming discrete energy level occupation states in the transverse direction. Control gate 43 is used to induce a depletion region 44 under the gate. The gate bias voltage V results in a depletion width d thorough the field effect according to:d=(2∈sV/eN)1/2 Where e is the electron charge, N the doping concentration in the channel and V the gate potential. A modulation of the gate voltage ΔV will result is changes to the depletion layer size Δd:Δd=d(ΔV/2V)The electrons are confined laterally by the depletion layer 44 and high resistivity areas 42 and 49 thus forming narrow conduction channels having a width depending on the gate bias. An applied external magnetic field B will induce a phase in each channel according to the AB effect which depends on the effective area as well. The gate voltage change results in a change of the effective channel area AA. In this manner the transmission is modulated according to:|T|2=cos2{e/(h/2π)·A/2·B(1+ΔA/A)}Thus the control gate is used to modulate the device source to drain current by controlling the cannel width.
FIG. 8 is a schematic band diagram of the device of FIG. 7. The electron population occupies the energy states above the conduction band edge and below the Fermi level. The electron allowable occupation states are divided to two separate regions by the said depletion layer thus forming two conduction channels marked 47a and 47b. 
FIG. 9 is a quantum interference device operated as a photo detector in the prior art [3]. Electrons travel from the source region 50 to the drain region 54 through a conduction region 52 which is laterally confined by a high resistivity area 51 and a depletion region induced by a control gate 53, thus forming two spatially separated conduction channels. The control gate is used to modulate the device current, as mentioned above, by controlling the conduction channel width.
FIG. 10 is a schematic band diagram of the device of FIG. 9. a Photon, having an energy hν, greater energy than the band gap energy (Ec-Ev), is absorbed to excite an electron hole pair. The holes are attracted to the gate region as the valance band level there is higher in energy and modify the potential under the gate. As a result, the depletion layer shrinks as indicated by dotted lines and the effective area A is reduced, thus affecting the drain current and resulting in a photo current ΔiG. Since the drain current is changed by the photon absorption a photo detector operation is attained.
FIG. 11 is a schematic diagram of a light interferometer having either a monochromatic or a white light source. An interferometer is a commonly used apparatus to produce interference patterns of light. A source 57 emits either monochromatic or white light having a propagation direction as indicated by the wave vector 59. This incident wave encounters a beam splitter 64 which transmits about half of the energy laterally as indicated by 60 and reflects about half of the energy vertically in the direction indicated by 63. The waves 60 and 63 encounter reflective mirrors marked 65 and 58 respectively. The resulting reflected waves propagate in the directions marked 61 and 62 back to the beam splitter where, after being reflected once again, they advance as 66 and 67 to a display screen 68. Since the source 57 emits energy in a continuous manner, the result is a standing wave within the apparatus which is a sum of all the propagating and reflected waves. The mirror 58 is of a fixed nature while 65 may be moved along the lateral axis as indicated by the deflection d. The said standing wave may have either a constructive or destructive interference depending on whether the path difference 2d is either an even or an odd multiple of the emitted light half wavelength.
Furthermore, the apparatus size L must be kept smaller than the coherence length of the emitted light. The coherence length is a measure of how far the phase information of the emitted wave is kept consistent as it propagates through the apparatus and is given by:U=c/νWhere c is the speed of light and ν is the light frequency.
When the mirror 65 is displaced by distance d, the effective size of the apparatus changes and a constructive or destructive interference occurs as a function of d. If the source is of a monochromatic nature, the resulting pattern can be seen on the screen 68 as a cyclic pattern of light intensity depending on d. However, if the source emits white light, the resulting pattern resembles the one seen on screen 69. The reason is that in the case of white light only a perfectly symmetrical apparatus would result in a zero phase difference between the lateral and vertical path sections which allows most of the energy to be transmitted through, regardless of the light wave initial phase. Once the mirror 65 is displaced in any direction away from its optimal location, a sharp drop in the transmission of energy through the apparatus occurs.
The basic concept of particle wave duality introduced by quantum mechanics is still in agreement with the classical theory of the interferometer mentioned above. Even when the light source is replaced by a single photon source, emitting a single photon at a given time interval, the intensity pattern as seen on the screen is still consistent with the classical picture. The underlying theoretical explanation views the photon as if having an interference with itself as it passes through the apparatus thus having a transmission probability. If the lateral and vertical path sections are unbalanced, resulting in a half wavelength difference, the classical condition for a destructive interference, the transmission probability of the photon would drop significantly. If, on the other hand, the apparatus is perfectly balanced, the transmission probability would be close to unity, regardless of photon coherence or initial phase, a situation similar to the classical white light source case.
It has been demonstrated by several experiments, given herein as a reference, that interference patterns of the well known double slit experiment could be achieved with fermions, being electrons or ions, and even complex molecules such as C60. These experiments utilize a source where a single particle is emitted at a given time interval, which still result in the known interference patterns, thus further enforcing the quantum mechanical view of the wave particle duality known as the “Copenhagen Interpretation”. The coherence length in this case depends on the particle De Broglie wavelength having a tighter restriction on the apparatus physical dimension.
FIG. 12 is showing the theoretical carrier population density as a function of energy for fermions in a lattice. The conduction and valance bands are marked as Ec and Ev respectively, while the Fermi level is marked as Ef. The density of states function describes the availability of states in the reciprocal space and has a square root dependence on the energy in three dimensions space. The Fermi Dirac function (FD), which has an inverse exponential dependence on the energy, is marked ƒ and gives the occupation factor for electrons in the conduction band as a function of temperature and energy. The occupation factor for holes in the valance band is according to 1−ƒ. The carrier population is a result of a multiplication of the FD function and the density of states for both electrons and holes and can be seen in FIG. 12 as well. The average electron kinetic energy is equal to ½kT for every motion degree of freedom and is derived using the following expression:Eavg=∫E·n(E)·dE/∫n(E)·dE 
The QID of the prior art presented here have a complex structure, a fact that makes them unsuitable for use in high volume integrated circuits. The active area where the AB interaction takes place must be kept small while the supporting structure is very large in comparison. This overhead is extremely costly and area consuming and cannot be tolerated in state of the art integrated circuits. The further complexity of the layered structure presented in some of the prior art devices requires a special process which is even more costly and does not integrate easily with the widely used silicon process. Furthermore, some prior art QID are operated using an external field to produce the resulting current modulation, which adds further difficulty and makes it impossible to use them along side conventional switching devices, such as MOSFET, where such a field would compromise their functionality. In addition, prior art QID are designed to operate using either an electric or a magnetic field or a photonic interaction. None of the prior art QID have a disclosed structure able to produce the same functionality regardless of the interaction type.
The background and associate prior art erase procedures are described in the following publications: [I] Journal of Vacuum science and Technology, vol. 6 January/February 1998, pp. 131-133, Mankeiewich et al., “observation of Aharonov-Bohm effect in quasi-one-dimensional GaAs/AlGaAs rings” [2] Applied Physics Letters, vol. 48, February 1986, pp. 487-489, S. Datta et al., “Proposed Structure for Large Quantum Interference Effect” [III] Applied Physics Letters, vol. 57 no. 21, November 1990, pp. 2231-2233, M. Okuda et al., “Novel Electron Interferometers using field induced decoupling in double quantum well structures” [IV] Feynman R., “The Feynman Lectures on Physics”, vol. III, ISBN 0-201-02118-8P [V] Markus A. et al., “Wave Particle Duality of C60 Molecules”, Nature, 14 Oct. 1999 [VI] Donati O. et al., “Experiment on Electron Interference”, American Journal of Physics, vol. 41, pp. 639-644.